I have gotten my shaman to the last boss with a friend tanking on a DK. Basically what happens with the insanity phase is each toon gets ported into their own little world and has to kill the evil persona's of the rest of the group, including themselves. So each toon has to kill 5 people (at least I thought it was 5... could be wrong tho lol) with around... 4k health I believe on normal. My only thoughts on how to complete the boss would be to have your highest dpsing toon (probably your mage) kill all the guys first, bc as soon as one kills them, then they move on to help everyone else kill the other guys. (Keep in mind this boss does the insanity phase twice.) While the mage works on killing everything I would set up a button to have each toon that can heal, heal themselves. That way they can survive while the mage comes thru and dps's the guys down. So mage kills their 5 guys, then say the mage can go help the priest healer, and after the priests 5 guys are down use the priest to help dps as well on w/e group member is available next, while the other keep healing themselves.

Granted, this is just a theory I came up with, I've never actually tried it. But in theory it should work (granted mana be available of course) bc after one toon kills their 5 guys they are available to help the other group members. But if you want to create some ideas of your own for this boss fight, I'd recommend checking out this which is what WoWWiki says about the boss. And actually, the agree with my idea as far as healers in the normal group set up are concerned, just heal your way thru the dmg until the other group members can help you. So hopefully this will work for us boxers!

Oh, and one last little thing I just read on WoWWiki... "If you're having difficulties with the insanity spell a good strategy is to tank Volazj near a pillar, and when he casts insanity everyone ensures they are not within line of sight of Volazj by running around the pillar. This way the insanity debuff will wear off after a couple of seconds and you won't have to fight anyone." This might help us as well. It just make take a few trys to get it done right.

Good luck! And hope this helps